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Electrodynamic heads with flat diaphragms. Acoustic systems ch2 "Surround" wall acoustic systems

The standard dynamic speaker we know today was developed in the 1920s and uses a magnetic field to move a coil or magnet that is connected to a diaphragm. Of course, there are other types of speakers that depend on the type of amplification device, in addition to standard round speakers, in this article we will look at a few basic types: horn (horn), piezoelectric, magnetostrictive speakers, electrostatic, ribbon and flat magnetic speakers, wave, flat panel speakers, "air traffic converters", plasma speakers, and digital speakers.

1. Horn (horn) speakers

These speakers were the very first form of sound amplification. They don't need electricity to amplify. These speakers have been used in their designs for example: Thomas Edison, Magnavox, and Victrola. The period of their use is approximately 1880 to 1920.

Their main drawback is that they cannot produce high-quality and powerful amplification. In the future, they will be completely replaced by speakers and devices based on electricity. Today they are interesting only as an exhibit for collectors, although there are modern developments that fully or partially use the principles of horn speakers.

2. Electrodynamic (modern) speakers

What is an electrodynamic speaker? It is a device that uses an electromagnetic coil and a diaphragm to create sound. This is the most common type of speaker in the world today.

How it works?

A modern speaker uses an electromagnet to convert electrical signals of varying strengths into cone movement. A coil of copper wire moves in a magnetic field. It works using the principle of induction. The coil is connected to a cone made of cardboard, paper, vinyl or other material. The diaphragm cone vibrates with the electromagnetic coil. Sound is created and amplified directly by the diaphragm itself. The peculiarity of these speakers is that each type of speaker is produced for a specific frequency range, because it depends on the type of magnets, material and purpose of the speakers.

A little about the sound:

Sound is a form of energy that travels through a gas or liquid. There are two main parameters for measuring sound: frequency and volume level (decibels). Frequency is responsible for the sound quality in the speaker, decibels for the loudness of the sound.

People can hear sound with a frequency of 20 - 20,000 Hz. Hertz is the number of cycles per second. Sound is a wave in the range from 0 energy level to infinity.

If you look at music, then any note does not sound at a constant frequency, it is a sound wave that reaches its maximum, for a note C sharp of 1 octave, for example, every 277-278 times per second. The frequency spectrum perceived by a person is (approximately) from 20Hz to 20 kHz,
the highest sensitivity in the range from 2 to 4 KHz.
Dynamic range (from the quietest perceived sounds to the loudest) about 96 dB (more than 1 in 30,000 on a linear scale).
It is generally known that a person is able to distinguish a frequency change of 0.3% at a frequency of the order of 1 kHz.
If two signals differ by less than 1 dB in amplitude, they are difficult to distinguish. The amplitude resolution depends on the frequency and the highest sensitivity is observed in the range from 2 to 4 KHz.
Spatial resolution (ability to localize the sound source) - up to 1 degree in humans.
Sounds of various frequencies spread through the air with different speed... As a result, the high-frequency part of the spectrum from a source located at a distance from the listener is somewhat delayed.
A person is not able to notice the sudden disappearance of high frequencies if it does not exceed about 2ms.
Several studies show that humans are able to sense frequencies above 20kHz. With age, the frequency range narrows.

For human speech, information-carrying frequency spectrum: 500 Hz to 2 kHz
Low frequencies in our speech are bass and vowels, high frequencies are consonants.
Since a neuron can be fired no more than 500 times per second, then to obtain information about higher frequencies hearing aid a person resorts to some "tricks": at frequencies up to 500 Hz - the vibrations are directly transformed into nerve impulses.
Up to about 1.5 kHz, the problem is solved by simultaneously connecting up to 3 neurons to one nerve ending. In this case, neurons are excited sequentially, one after the other and, accordingly, help to improve the frequency resolution by 3 times.
At higher frequencies, only the signal amplitude is recorded.
Thus binaural hearing, which plays an important role in localizing the sound source, is best developed at frequencies below 1.5 kHz. Above this frequency, the only source of position information is the difference in signal amplitudes for the left and right ears.

The main stages in the development of modern speakers:

1861 - The simplest type of electronic loudspeaker was developed by Johann Philipp Reis, a teacher in Friedrichsdorf, Germany. The speaker was capable of reproducing sound very coarsely. This was the first experience of using an electrodynamic loudspeaker.

1876 - Alexander Graham Bell also experimented with creating a speaker based on Reis's work.

1877 - Werner von Siemens' idea of an electromagnetic coil for use in speakers, he used it to convert input signals direct current telegraph. He did not have a solution for sound amplification, but he suggested that it could eventually be done in the near future.

1877-1921 - Various inventors and engineers work with the idea of electrodynamic loudspeakers, but so far they have been able to create only rough, distorted sounds. The industry continued to produce horn speakers.

C.W. Rice of General Electric and E.W. AT&T's Kellogg worked together in Schenectady, New York to improve electromagnetic speakers and the first electrical amplification system. They built a working prototype in 1921. Rice and Kellogg were able to finally solve all the problems that led them to a good, crisp sound. Previous attempts to make a loudspeaker produced poor, unacceptable, muffled sound. This muffled sound was not good enough to compete with the horn speaker sound that was well known in the market. Rice and Kellogg were able to fully understand what is needed to reproduce all the frequencies needed to create an accurate sound. Their prototype was large enough dynamic range frequencies to be better than the range of the horn speaker, while still being able to significantly increase the volume. In 1925, they applied for patents and gave a speech in St. Louis at the AIEE conference ( American Institute of Electrical Engineers). After several years of work, they refined it as the first commercial product of its kind and named the Radiola No.104 loudspeaker. It sold in 1926 for $ 250 (about $ 3000 today). The speaker was marketed under the RCA brand.

Electrodynamic loudspeakers are now manufactured for several purposes and are divided into main categories:

Tweeters ( Tweeter) - 2 kHz - 20 kHz, used for the production of the entire upper range of tweeters. Most tweeters are made on the principle of electrodynamic loudspeakers, however there are piezoelectric, electrostatic and plasma tweeters.

Midrange speakers ( Mid-range) - 300 - 5 kHz. This range covers most of the human voice along with most musical instruments.

Subwoofer ( Woofer) - for frequencies 40 - 1 kHz.

Subwoofer ( Subwoofer) - 20 - 200 Hz. Very low frequencies. The human ear can only hear up to 20 Hz. low frequency range. This means it can be placed anywhere in the room and heard from anywhere with the same sound quality. Subwoofers also produce sound waves that travel easily through walls. Noise from this type of speaker can even penetrate vertically through 5 or more concrete floors in residential buildings. Needless to say, it's easy to get into trouble with local noise ordinances. Subwoofers were developed in the 1960s.

3. Flat panel speakers

This is where NXT technology stands out.

NXT panels- This is one of the variants of execution of flat panel loudspeakers. The basis was the development for the military industry, however, the main application of such devices was found in consumer electronics. Parrot uses this technology in MINIKIT SLIM, MINIKIT CHIC and MINIKIT L.E.

Speaking about the features that distinguish the system favorably, we should name those that are important when using the device in a confined space:

practically flawless sound emission in all directions;
low dependence of acoustic pressure with distance from the NXT panel. That is, the sound quality does not drop when the user moves.

Unlike conventional loudspeakers, NXT is a flat panel technology where it is driven from a single point using a moving coil, piezoelectric element, or other driver. The NXT drive maximizes the resonant behavior of the panel, for example, by selecting the surface material and locating the exciter.

The main idea is to get the most random nature of the movement of any two adjacent points of the panel surface relative to each other - and this is the main breakthrough of NXT.

In the very rigid panel of the NXT system, after excitation based on the usual electrodynamic or electrostatic principle, complex vibration processes occur over its entire surface. In this case, the resonance properties associated with the structure of the material and the point of excitation become more intense, the adjacent elements of the material begin to vibrate arbitrarily. The scientific name for this phenomenon is "distributed vibration mode". Try to imagine a downhill track where bumps turn into grooves and vice versa. It is necessary that the structure of vibrations in the entire frequency range be as complex and dense as possible.

Unlike conventional multi-way loudspeakers, a single NXT is used to reproduce the entire audio range, driven by a single transducer. With an area of 0.6 sq. m, the lower cutoff frequency is 100 Hz, and the upper cutoff frequency is 18 kHz. And the deviations of the frequency response are in the same order as that of conventional loudspeakers. With an increase in the area up to 1.5 sq. m the low-frequency limit is reduced to 60 Hz. NXT panels can handle sizes from 25 sq. cm up to 100 sq. m! The smallest ones can be used in a multimedia system together with a laptop, and the largest in cinemas, serving as a screen at the same time. And at the same time, a completely endless sea of applications opens up from automotive acoustics and portable devices(Parrot MINIKIT SLIM) to completely invisible (for the eyes, but by no means small) built-in acoustics, imitating even architectural fragments of a room.

NXT panels can handle sizes from 25 sq. cm up to 100 sq. m! The smallest ones can be used in a multimedia system together with a laptop, and the largest in cinemas, serving as a screen at the same time. And at the same time, a completely boundless sea of applications opens up from car acoustics in the form of a shelf under the rear window to completely invisible (for the eyes, but by no means small in size) built-in acoustics, imitating even architectural fragments of a room. Speaking of the parameters that favorably distinguish the system, one should first of all mention the almost impeccable sound emission in all directions, the quality of which is somewhat reduced at low frequencies in comparison with classical diffuser loudspeakers. In addition, the acoustic pressure is significantly less dependent on distance from the NXT panel. And if the sound pressure measured by traditional methods at a distance of 1 meter is 4 dB less than that of an average dynamic loudspeaker (for which we take 90 dB SPL), then when moving 3.5 m for the NXT it will decrease by only 4 dB against 11 for acoustics with traditional signal source transducers. So when the listener moves around the room, it is almost impossible to detect any changes in either the frequency spectrum or the loudness. During the demonstration, turning the panel 90 ° or placing it behind the back of the person demonstrating it had virtually no effect on the playback quality. Due to microscopic movements, the impedance character of the exciter for the panel will be simply resistive, which greatly facilitates the operation of the amplifier.

The NXT system has virtually no power limitation, although the temperature of the transducers still has to be controlled. On the other hand, the panels themselves act as a cooler at the same time. Moreover, the shape of the panel can be adapted to the stand on which it will be placed. At the same time, one should not forget about energy losses on one side of the panel. The subjective impression of the sound of the NXT system panels can be described as transparent with detailed recognition and transmission of short-term signals without distortion. With regard to Hi-Fi playback, the relative disadvantages include some limitation of the low frequency band, as well as the loss of accurate localization. These disadvantages are caused by the so-called “diffuseness” of the sound field, which is not a disadvantage in itself, and for the rear acoustics of a home theater THX is even necessary, but nevertheless it can be eliminated in the process of improving the NXT system.

4. Membrane columns

The principle of operation is that magnetic fields are used to move the sound-reproducing element (diaphragm). In this kind of dynamics, the coil is mounted directly to the diaphragm. The main advantages of such speakers are high power, wide range of reproducible frequencies and compact, especially in thickness, dimensions.

5. Plasma arc columns

Plasma is an ionized gas, or current in a gas. Plasma reacts to electric fields so you can turn an electrical signal (sound) into an electrical field that manipulates the plasma. Plasma has mass and will vibrate to create sound, similar to how air moves through a diaphragm to produce sound. These speakers are visually interesting, but limited in sound quality. Such developments have reliability problems and therefore remain only as a concept or devices for amateurs.

6. Piezoelectric speakers

Piezoelectric speakers are limited in frequency response so they
used only as tweeters (tweeters) in small electrical devices such as clocks to reproduce simple sounds... These speakers are made with solid-state technology, which makes them very durable, making them an excellent solution for use as a microphone underwater. In them, sound waves are created by changing the geometry of a rigid and elastic, most often flat, element, usually made of piezoceramics (such as barium titanate). These emitters reproduce sounds well at resonant frequencies and hardly reproduce at all others.

7. Electrostatic speakers

High-end loudspeakers include electrostatic loudspeakers, affectionately referred to as electrostats. Their principle of operation is simple - the attraction of a flat membrane to a strained plate. Alas, for a noticeable manifestation of this effect, one has to use very high voltages - up to about 10 kV. But even in this case, the effect is so weak that in order to obtain an acceptable sound volume at low frequencies, the membrane area must be of the order of 1 square meter, or even more, which determines the large dimensions of the loudspeakers. It is gratifying that even though their thickness can be small - about 10-15 cm. Of course, designers have to remember about safety measures when working with such high-voltage units. Sony is one of the few stubbornly leading the development of electrostats. The dimensions of the speakers (1.5 meters high and 0.8 meters wide), as well as the operating voltage of 9 kV, speak for themselves. But the speakers reproduce low frequencies well - for this they use two membranes measuring 50 × 27 cm. The smaller membranes are used to reproduce medium and high frequencies. Electrostats are not only bulky but also very expensive emitters. It is unlikely that they are of practical interest for the vast majority of our music lovers and electroacoustics lovers. As well as some types of emitters that use special physical effects leading to the generation of sounds, for example, the generation of sound vibrations by plasma. However, the picture changes if electrostats are used only for reproducing mid and high frequencies, and the honorable mission of reproducing low frequencies is left to well-proven dynamic loudspeakers. Sony also followed this path, using HF electrostats in a number of its music centers. The range of effectively reproducible frequencies extends from the lowest frequencies of the audio range to tens of kilohertz (it is curious that the firm has not yet indicated the exact data). All experts unanimously agree that these systems give a particularly transparent and natural sound, the quality of which is impossible to find fault with.

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According to the theory of inventive problem solving (TRIZ) the best device is the one that is absent altogether, and the task is completed. So it is with home electronics - many are not averse to minimizing its presence. This is especially true for speakers. There are many reasons. The most common of these are children, who can accidentally knock over the speakers; expensive square meters consumed by technology; blocking up passages, etc. Well, in commercial objects - shops, restaurants, etc. in general - a real salvation.

A laconic solution in this situation is wall acoustic systems... In the minds of many, these are still ordinary shelf speakers that are screwed on scary brackets. In fact, now there are a lot of wall-mounted acoustics of very different designs, different sound quality and, of course, different prices. Hope this short review it will be useful to get a general idea of the existing possibilities. This review is primarily about design. Well, technical nuances can be found in our Gallery.

Flat speaker systems.

They are usually rectangular in shape. Among them there are very thin ones - only 2-3 centimeters thick, and there are also quite voluminous ones, there are the size of a notebook, and the size of a human being. The main question here is the sound quality and power that you need and which is appropriate for the size of the room. Some of wall models sound at the level of a radio point (who remembers), and some correspond to the level High end... In terms of finishing of flat speakers, their main difference is the color of the frame and the color of the grill.

Flat models with images printed on the grill are quite popular. In fact, they disguise themselves as paintings. In order for such an imitation to be complete, baguettes are sometimes ordered as tuning - from simple to luxurious. But the ability to use them depends on the design of the speakers.

Some flat acoustics shouldn't be masked. Thanks to the high-quality finish, it can make good friends with many interior styles.

"Surround" wall-mounted acoustic systems.

The disadvantage of flat speakers is that they require a certain amount of space on the wall, and the higher the speaker level, the more space they usually require. You can't go anywhere - physics. Therefore, an alternative can be “volumetric” wall-mounted speakers. They not only save space on the wall, but also look pretty impressive.

The choice of shapes and materials is very large here. But the “size rule” is also respected. More powerful and high-quality speakers, as a rule, have larger dimensions. But "kids" should not be discounted either. A properly selected compact solution is quite capable of coping with the tasks at hand. Typically wall-mounted speakers work in conjunction with subwoofers. Although the subwoofers are located mainly on the floor, they are less conspicuous and less critical to the location, however, there are certain requirements here.

Among the "volumetric" wall models, there are representatives of "soft" forms that can fit well into the "classics" and modern interiors. Some of them are not originally wall-mounted, but can be wall-mounted.

There are also models built on rigid straight lines. As a rule, they are better “friends” with minimalistic interiors and some neoclassical trends, where straight lines also prevail.

Soundbars

It is customary to place this type of speaker systems on the walls. Mostly soundbars are used in low-cost home theater systems. In terms of sound quality, it is difficult to demand anything special from them. Rather, they are designed for a completely unassuming user. In most cases, the design is also focused on budget modern interiors.

However, there are real "kings" among the soundbars. The dimensions of such speakers exceed two meters and in fact completely replace full-fledged high-end floor-standing speakers.

The decoration of such systems is also different. But in most cases, you can find an option for both classics and high-tech.

Rear speakers.

Such acoustics are used in home theaters for rear and sometimes side channels to create surround sound. In many ways, the design approaches are similar to the flat and surround speakers described above. The difference is that the purpose of such acoustics is quite definite - to create surround sound effects in a home theater. Although in some cases they are used as the main speakers in small rooms. From the point of view of "strict rules" this is not true, but for an inexperienced music lover this can be a solution in terms of design with acceptable sound quality.

Naturally, in order to achieve the optimal result according to all criteria when using wall-mounted speakers, it is necessary to work together both the customer and the interior designer and specialists in this technique. The gallery of impeccable electronics "Nazarov" has accumulated extensive experience in using wall-mounted acoustic systems different types in a variety of interiors. Surely we will find the optimal solution for any, even the most non-standard case. Contact us, we will be happy to help you!

The review was prepared by Oleg Kostyuchenko.

While our industry was setting up the production of Electronics 100AC, progress in the West did not stand still, new speakers with coaxial, isodynamic, electrostatic loudspeakers were introduced. The largest Japanese corporations - Sony, and then Matsushita (Technics), began to develop completely new dynamic heads operating in a piston mode. The main distinguishing feature of these speakers were completely flat, rather than cone honeycomb cones. A flat emitting surface does not have resonances inherent in cones, has no stress zones and is phasaline in itself and is closer in nature to musical instruments.

Already in 1978, Sony presented a prototype of the most high-tech speaker system in the world - the Sony / Esprit APM-8. The diffusers of all four speakers are square in shape, the woofer had as many as 4 cobalt, core powerful magnetic systems that moved a single flat cone like a piston. Then, an earlier not reproduced by any speaker, deep bass at 25Hz at a level of 8db was achieved, and sow a day an unattainable low THD in the low-frequency region, which even at 40Hz does not exceed 2%!

Sony / EspritAPM-8 (1978)4 stripes, multi-amp capability, anti-diffraction coating, 102kg. 500W. 25-30 000Hz.

Inexpensive but high quality flat honeycomb emitterTechnics. (used in the Technics SB-7)

TechnicsSB-10 isodynamic HF emitter, cellular midrange with "invisible" suspension, honeycomb woofer (32cm) with coil extra large diameter (160mm). The magnet and two centering washers are inside this coil! It turns out like a speaker inside out. Such a complex design was produced only by Technics and then for a short time.

The Lo-D company (Hitachi concern) did not follow the path of Sony and Technics and developed its own flat diaphragms, but not of a honeycomb structure, but filled with synthetic foam and a velvet acrylic coating on the emitting surface, the same Lo-D diaphragms were used for the manufacture of passive emitters.

Trio (the high-end audio division of Kenwood) used cone woofers reinforced with honeycomb ribs. The acoustic design was a special horn phase inverter, which occupies the entire back part AC. MF / HF drivers Trio produced with flat carbon fiber diaphragms, impregnated with acrylic resins.

JVC in its speakers (Victor Zero-7) has developed cones entirely from a composition of foam resins. In the design of the speakers, the suspension was fixed on the back side and was "invisible". The innovation consisted in the fact that the reflections of the sound waves disappeared from the edge of the suspension, which, in the standard design, return back to the diffuser. The three bands of such speakers were complemented by an ultra-light ribbon supertweeter with an acoustic lens.

Lo-D HS-5000 (Lo-D Division of Hitachi, Specializing in high-end equipment)

Flat emitterLO- D, diffuser filled with special foam and laminated with metal.

Flagship model of the company Technics - SB-M 1 (1981) 4 bands, honeycomb emitters - a kind of answer to Sony / Esprit APM-8, only more than half the price .

The honeycomb filling of the diffuser gives incredible stiffness with the highest coefficient of internaldamping, while it has a low mass.

Trio LS-1000, rear panel is the mouthpiece thatinteractswith roomfor listening, what raisesbestowallow frequencies.

OnkyoScepter-300, the rear panel with the appearance of a conventional speaker has 6 multidirectional midrange-high frequenciesemitters, which, according to the developers, gives the feeling of a complete 3-dimensional picture of the sound image.

VictorZero -7. Due to the use of flat emitters, even in a multiband design, minimal phase correction is sufficient.

Diatone DS-505, 4 bands, cone woofer diffusers - honeycomb construction, dome - super light titanium boron.

At the turn of the 70s-80s, after lengthy experiments and research, many designers came to the conclusion that an ideal emitter is a point source of sound. In such a loudspeaker, phase and transient distortions are minimized, the sound is emitted from one point without the separation of the band-pass speakers (LF, MF, HF) in space. That gives the listener the feeling of being fully present at the concert, the sound is not tied to the speaker, and all virtual sources are precisely localized in space. Wide-range dynamic drivers are not able to reproduce well the entire audible frequency range, especially in the high-frequency part. Therefore, the developers began to install several loudspeakers on the same axis. The most interesting solutions were used by Tannoy and Altec Lansing.

Tannoy used large paper woofers with an acoustically transparent dust cap and a tapered hole in the core through which the tweeter emitted, mounted inside the woofer magnet system and powered by its magnetic field. The main disadvantage of this concept is the oscillation of the low-frequency cone, which simultaneously serves as a horn for the high-frequency.

TANNOY Autograph (K3808) (1979) specially designed for corner placement. Acousticdesign - the front part of the speaker is loaded onto a horn, the back part is loaded into a labyrinth of complexforms.

Coaxial speakerTannoy... The dome tweeter is located inside the cone woofer and uses its own magnetic field only on the other side of the magnetic system.

Altec Lansing 620B Monitor, 1978The HF driver is attached to the back of the large 15 "woofer and radiates through a hole in theits core to its own horn.

It wasn't until the late 1980s that Technics was able to fully implement point emitter theory in its SB-RX Series speakers. In addition, the Technics spot emitter operated in piston mode and was completely flat.

I would like to note another significant idea at the turn of the 70s and 80s. This is a mechanical feedback system (EMOS) developed by Philips. Everyone knows that amplifiers with a high output impedance very lively and naturally transmit the mid and high frequency spectrum of a music signal, and amplifiers with a low output impedance (which causes a high damping factor) play out bass well and accurately. Philips engineers have placed a micro sensor on the woofer diffuser that monitors amplitude, temperature, power and other parameters. The data is then sent to a microprocessor that controls the amplifier installed in the speaker cabinet. Based on the information received, the microprocessor adjusts the output impedance of the amplifier. When implementing multiband amplification, the design is freed from passive crossovers, in which part of the signal is lost. It becomes possible to change the parameters of the amplifier, as it is necessary in this moment time.

I am writing this note with somewhat mixed feelings. On the one hand, the technology about which information has appeared is very interesting and can in many ways turn modern views in the field of its application. On the other hand, this information is more advertising than practical, since I could not get direct evidence or some examples. Well, time will tell, but for now - that's what we're talking about.

Warwick Audio Technologies declares that it has developed completely flat acoustic speakers (sounders) according to new technology... The company claims the following characteristics:
- speakers look like flat polymer sheets, sizes vary from A5 to A3
- sheet thickness is 0.2 millimeters
- flexible sheets
- provided sound pressure - from 85 to 105 dB (this number, apparently, refers to the measurement of pressure directly at the surface of the sheet)
- provide a very high directionality of sound due to the focusing of the sound wave by bending the sheet (like a curved mirror reflecting light from different directions to one point)
- extremely low current consumption, high efficiency and negligible thermal imaging
- not influenced by external magnetic fields

The company does not hide the fact that their technology is a development of the ESL technology that has already existed for several decades - Electro Static Loudspeaker (electrostatic sound emitter). ESL refers to a speaker design where sound is generated by a membrane placed in an electrostatic field. I quote from wikipedia:

In the most common version, a high-resistance diaphragm is placed between two stators. A high voltage is applied to the membrane relative to the stators, a high amplitude signal is applied to the stators (high voltage sound signal). As a result, an alternating electrostatic field is generated between the membrane and the stators, which moves the membrane. The field acts uniformly on the entire membrane, and the membrane has an extremely low mass, thanks to which high characteristics are achieved: coeff. nonlinear distortion reaches 0.05%, high impulse response, flat frequency response.

Warwick Audio Technologies' technology is called FFL ("Flat Flaxible Loudspeaker"). It implements the same idea as the already developed electrostatic speakers - a sound wave is created by a flat membrane oscillating in an electrostatic field. However, the company's innovation lies precisely in the fact that they managed to make the structure surprisingly flexible and thin. In fact, the company did not create some kind of electromechanical structure, but a completely homogeneous laminate material. A laminate sheet consists of three layers - two membranes and an insulating layer between them.

When the upper diaphragm is "rocked" by an electrical signal, the diaphragm vibrates exactly in phase in all its sections, forming something similar to a piston. Thus, the sound wave generated by the movement of the membrane is very directional.

The company, of course, does not disclose more detailed details of its development.

If all this is true, then such speakers will find their application in countless places and situations: in the subway over the heads of passengers, in supermarkets right in the pictures of products, in cars, in offices, etc. and so on.

By the way, Warwick are not the only ones who have announced such sound emitters. More recently, another group of developers, this time from the Industrial Technology Research Institute, presented to the public their development in the same area - Flexspeakers. there is a video clip showing such a speaker in action. ITRI promises that their A2 size acoustic sheets will be available commercially for as little as $ 20 very soon.

You can share your thoughts in the comments to the note.

The development of flat honeycomb loudspeaker heads began in the 1980s, but loudspeakers using them have only recently become available. Last year, our magazine has repeatedly introduced radio amateurs to acoustic systems of various classes based on cellular heads, which are produced by the St. Petersburg firm "Sound". This information interested many readers who asked to tell in more detail about the advantages of such heads, to give the parameters. Meeting their wishes, we publish an article by former employees of VNIIRPA im. A.S. Popov, engaged in the development of heads with honeycomb diaphragms.

Many factors are known to affect the sound quality of a speaker, but it primarily depends on the speaker heads used in them. Considering these circumstances, experts in electroacoustics pay close attention not only to improving the designs of moving head systems, but also to the materials of the emitting elements.

As a result, flat-diaphragm heads have become widespread in recent years along with traditional cone diffusers.

The main requirements for the physical and mechanical parameters of the materials of the radiating elements are, as you know, high bending stiffness, low density, and high internal losses. The higher the first of the named parameters, the wider the frequency range of the head and the less the amplitude-frequency distortions it introduces into the signal.

The density of the material of the radiating element largely determines the sensitivity of the head and, finally, internal losses contribute to the damping of oscillations at resonant frequencies.

For decades, paper pulp has been used to make cone cones for drivers. With the development of Hi-Fi technology, leading manufacturers of high-quality speakers in order to increase the modulus of elasticity and losses of head diffusers began to use for their manufacture all kinds of composite materials based on cellulose (for example, cellulose with carbon or metal fibers).

However, it was not possible to significantly increase the rigidity of such materials because of the small internal elastic forces connecting the components.

For this reason, polymeric materials such as mylar, polyamide, polypropylene, polyvinyl chloride, olefin films, tergal, supronil, ceramic olefin, polymer graphite, etc. have begun to be used for the manufacture of low-frequency, mid-frequency, high-frequency heads of high-quality speakers. for these purposes composite materials (bextren, kobeks, kapton), as well as laminated materials mylar and polyester with aluminum spraying, two-layer polypropylene).

The development of the technology of chemical vacuum deposition made it possible to obtain a number of layered metals (titanium-boron carbide, aluminum-magnesium, aluminum-sapphire, etc.). For the dome-shaped diaphragms of the midrange and high frequency heads, simple metals are also used: aluminum, titanium, beryllium alloys, porous nickel.

Tab. 1. Basic specifications flat-diaphragm heads

Main technical characteristics	300GDN-1	200GDN	100GDN	25GDN	75GDS	50GDS	10GDV-5	25GDSH-2M
Characteristic sensitivity level, dB / W / m	90	88	87	87	92	89	91	87
Nominal frequency range, Hz	20..3150	31,5..4000	63..5000	70..6300	200..6300	250..6300	2000..31500	80..16000
Rated electrical resistance, Ohm	4/8	8	8	4	4/8	8	8	4/8
Maximum noise (long-term) power, W	200 (300)	100 (200)	75 (100)	25 (50)	50 (75)	25 (50)	20	25 (50)
Dimensions, mm	315*130	250*120	200*90	125*65	160*85	125*65	11011035	125*65

However, the production of many of the above materials requires very complex and expensive technological processes... In addition, they are not universal, that is, they cannot be used for the manufacture of emitting elements of all speaker links (LF, MF and HF heads).

For this reason, heads with radiating elements made from the materials listed above have not been able to replace heads with paper cone diffusers, and until recently remain just separate successful achievements of leading foreign companies.

The analysis of the properties of the materials of the radiating elements and the design directions of the loudspeaker heads for the Hi-Fi class speakers were constantly engaged in by the specialists of VNIIRPA them. A.S. Popova. The results of fundamental research carried out by them in 1980-1990. , have shown that a very interesting and promising direction in the design of dynamic loudspeaker heads is the use of flat honeycomb diaphragms as a radiating element.

One of the main advantages of this area is the suitability of such diaphragms for the design of bass, midrange, treble and even broadband loudspeaker heads, as well as the ability to create acoustic systems on them for all purposes, from automobile to Hi-Fi and High End speakers.

It is known that a flat honeycomb diaphragm has a three-layer structure: a honeycomb base made of aluminum foil, covered on both sides with sheathing made of sheet materials.

Three-layer honeycomb-based materials have been used in the aviation industry for many years. However, the specifics of the operation of the loudspeaker heads demanded the creation of new technological processes and special equipment for the production of honeycomb diaphragms.

Many years of experience in the design of flat honeycomb diaphragm heads have revealed a number of their advantages over traditional paper cone heads.

First of all, heads with honeycomb diaphragms reproduce a wider frequency range with minimal amplitude-frequency distortion. sound signal, which allows you to create on their basis speakers with uneven frequency response in the operating range of +1.5 dB. The use of honeycomb diaphragms makes it possible to significantly reduce nonlinear distortions.

On their basis, it is possible to create more powerful loudspeaker heads, since the heat from the voice coils is dissipated in them through the diaphragm into the surrounding space, while in heads with paper cones through the parts of the magnetic circuit it enters the speaker.

The flat surface of the honeycomb emitters does not require special measures to align the radiation centers, which greatly simplifies the speaker design.

The electroacoustic parameters of the honeycomb heads are less influenced by the temperature and humidity of the air, and are more stable during mass production.

Currently, the company "Zvuk" has developed a line of cellular dynamic loudspeaker heads. Their main technical characteristics are shown in the table. The appearance of one of the heads (100GDN) is shown in the figure. On the basis of the heads presented in the table, a number of AS ("Lyra", "Neva", "Rus") are produced, with which the readers are already familiar.

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